The present invention is directed to a stage assembly for moving a device. More specifically, the present invention is directed to a system and method for switching position signals during movement of a device table of a stage assembly.
Exposure apparatuses are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that retains a reticle, a lens assembly, a wafer stage assembly that retains a semiconductor wafer, a measurement system, and a control system. The reticle stage assembly and the wafer stage assembly are supported above a ground with an apparatus frame.
Typically, the wafer stage assembly includes a wafer table that retains the wafer, and a wafer mover assembly that moves the wafer table and the wafer between an alignment region and an operational region. In the alignment region, the wafer is loaded onto the wafer table and the positions of the chips on the wafer relative to the wafer table are determined. In the operational region, the images from the reticle are transferred to the wafer.
The size of the images transferred onto the wafer from the reticle is extremely small. Accordingly, the precise relative positioning of the wafer and the reticle is critical to the manufacturing of high density, semiconductor wafers. In order to obtain precise relative positioning, the reticle and the wafer are constantly monitored by the measurement system. Stated another way, the measurement system monitors movement of the wafer table relative to the lens assembly or some other reference. With this information, the wafer mover assembly can be used to precisely position the wafer table.
The measurement system typically includes one or more interferometer systems for monitoring the position of the wafer table. For example, a typical wafer stage assembly includes an X interferometer for monitoring the position of the wafer table along an X axis and a Y interferometer for monitoring the position of the wafer table along a Y axis. Each interferometer generates one or more position signals to monitor the position of the wafer table in both the alignment region and the operational region. Using the position signals from the interferometers, the control system controls the wafer mover assembly to precisely position the wafer table and the wafer.
Recently, wafer stage assemblies have been developed which have a longer stroke between the alignment region and the operational region. These wafer stage assemblies allow for more space in both the alignment region and the operational region. Because of the longer stroke of the wafer stage assembly, two X interferometers and/or two Y interferometers are necessary to monitor the position of the wafer table. In this design, the one X interferometer and one Y interferometer monitor the position of the wafer table when the wafer table and the wafer are in the alignment region and the other X interferometer and the other Y interferometer monitor the position of the wafer table when the wafer table and the wafer are in the operational region.
Unfortunately, the wafer mover assembly can abruptly and inaccurately move the wafer stage during the transition between the interferometers. This reduces the accuracy of positioning of the wafer and degrades the accuracy of the exposure apparatus.
In light of the above, there is a need for a stage assembly that precisely positions a device. Additionally, there is a need for a method and system for controlling the wafer mover assembly while switching between position signals of the interferometers. Moreover, there is a need for an exposure apparatus capable of manufacturing precision devices such as high density, semiconductor wafers.
The present invention is directed to a stage assembly that moves a device along an X axis and a Y axis between a first region, a transition region, and a second region. The stage assembly includes a device table, a X mover, a Y mover, a measurement system, and a control system. The device table retains the device. The X mover is connected to the device table and moves the device table along the X axis. The Y mover is connected to the device table and moves the device table along the Y axis.
The measurement system monitors the position of the device table. As provided herein, the measurement system includes a first X system and a second X system. The first X system provides a first X position signal that indicates the position of the device table along the X axis when the device table is in the first region and the transition region. The second X system provides a second X position signal that indicates the position of the device table along the X axis when the device table is in second region and the transition region.
The control system is connected to the movers and the measurement system. With this design, the control system receives the position signals from the X systems and directs current to the X mover and the Y mover to move the device table along the X axis and the Y axis between the first region and the second region with a plurality of servo cycles. To avoid an interruption in the position signal, both X systems provide a position signal in the transition region. This allows the first X system to be used to provide the position signal while the second position signal of the second X system is reset and offset to match the first X system. Only then is the positioning servo switched. Stated another way, the overlap between the first and second X systems in the transition region is used to reset and offset one position signal while the position servo uses the other. Only then is the position servo switched to the other sensor system. This switching is very fast so no servo cycles are stopped. As a result thereof, the control system does not abruptly move the device table during the transition between X position signals. Further, the stage assembly can be used in an exposure apparatus to manufacture high density, high quality semiconductor wafers.
Preferably, the X mover is moving the device table at a substantially constant velocity in the transition region. As a result thereof, there is no reduction in throughput of the exposure apparatus.
In an alternate embodiment, the control system does not direct current to the X mover during at least one cycle when the device table is in the transition region. In this embodiment, the control system can utilize the information taken from the previous measurement to fill the servo hiccup. More specifically, immediately before the transfer, the first X system provides the first X position signal that indicates the position of the device table to the control system. Further, immediately after the transfer to the second X system, the control system utilizes the previously measured first X position signal taken with the first X system. Subsequently, the control system utilizes the second X position signal taken with the second X system to control the X mover.
In another embodiment, the measurement system includes a third system that monitors the position of the device stage. In this embodiment, during the transfer between the systems, the control system relies upon the measurements taken with the third system to control the movers and the position of the device stage along the axis. More specifically, just before the transfer, the measurement system measures the position of the device stage along the axis with the first system and the position of the device stage relative to the guide assembly with the third system. Next during the transfer, the control system monitors movement of the device stage relative to the guide assembly with the third system. Finally, the control system uses the second system to monitor the position of the device stage along the axis.
The present invention is also directed to a method for making a stage assembly, a method for making an exposure apparatus, a method for making a device, a method for manufacturing a wafer, and a method for controlling the movement of a device table.